1. Field of the Invention
The present invention relates to a cleaning method and cleaning apparatus of a cleaning subject, and an electrophotographic photosensitive member and a method for manufacturing the same. The present invention especially relates to a cleaning method of optical parts, electronic parts, mechanical parts and precision parts, and a cleaning apparatus capable of cleaning the same, including an electrophotographic photosensitive member and a method for cleaning the electrophotographic photosensitive member comprising cleaning steps. The present invention also relates to a cleaning method by which fats and oils, fatty acids and resins adhered on the surface of a cleaning subject can be securely removed without using chlorinated solvents, and an apparatus to be used for these purposes.
2. Description of the Related Art
The method for manufacturing a substrate for use in an electrophotographic photosensitive member comprises the following steps.
The surface of a substrate for the electrophotographic photosensitive member is machined to a flatness within a prescribed degree by cutting with a diamond blade using a lathe or milling machine. The substrate subjected to surface machining is then cleaned with an aqueous solution of carbon dioxide, followed by depositing a film mainly composed of amorphous silicon to be converted into a deposition film of a photoconductive material by applying a glow discharge decomposition method on the surface of the substrate. While materials such as glass, heat-resistant synthetic resin, stainless steel and aluminum are proposed for use in the material for the substrate of the electrophotographic photosensitive member, metals are preferably used for the substrate material in most practical purposes, since metals are resistant to electrophotographic processes such as electrification, exposure, development, transfer and cleaning, thereby securing high positional accuracy in order to maintain image quality. Aluminum is one of the most suitable materials among them as a substrate for the electrophotographic photosensitive member, because aluminum is ready for machining, cheap and lightweight.
Technologies related to the substrate material of the electrophotographic photosensitive member are disclosed in U.S. Pat. No. 4,702,981 and Japanese Patent Publication Laid-open No. 60-262936. U.S. Pat. No. 4,702,981 discloses a technology for obtaining an amorphous silicon electrophotographic photosensitive member having good image quality by using an aluminum alloy containing 2000 ppm or less of iron (Fe) as a supporting member. The patent publication also discloses manufacturing steps for forming amorphous silicon by glow discharge after applying a mirror machining by cutting a cylindrical substrate with a lathe. Japanese Patent Publication Laid-open No. 60-262936 discloses an extrusion aluminum alloy being excellent in applying vacuum deposition and containing 3.0 to 6.0 wt % of magnesium (Mg), in which the contents of impurities are suppressed to 0.3 wt % or less for manganese (Mn), less than 0.01 wt % for chromium (Cr), 0.15 wt % or less for Fe and 0.12 wt % or less for silicon (Si), with a balance of Al.
Technologies for applying a surface machining to form a light receiving layer on the surface of the substrate depending on the application field of the electrophotographic photosensitive member are described in U.S. Pat. No. 4,735,883, and Japanese Patent Publication Laid-open No. 62-95545. Although U.S. Pat. No. 5,480,754 proposes a technology for cleaning the substrate with water, in which carbon dioxide is dissolved, for preventing corrosion in the cleaning step with water when an aluminum alloy is used for the substrate, no the process for recycling the water used for cleaning, consequently no flow rate of recycling water, is described.
Japanese Patent Publication Laid-open No. 5-61215 discloses the steps of circulating respective liquids in each cleaning vessel, continuously feeding a cleaning liquid into one vessel, allowing the cleaning liquid pooled in one vessel to overflow to transfer it to another vessel, and cleaning the substrate in each vessel. However, no steps for changing the circulation volume of water in the vessel in which the liquid overflows described.
While Japanese Patent Publication Laid-open Nos. 63-311261, 1-156758 and 7-34123 disclose a technology for forming an oxide film on the Al substrate, the step for circulating the cleaning water for repeatedly cleaning the substrate is not described.
Meanwhile, a variety of materials such as selenium, cadmium sulfide, zinc oxide and amorphous silicon, as well as organic substances such as phthalocyanine, are proposed in the technology of elemental materials to be used in the electrophotographic photosensitive member. A non-crystalline deposition film represented by an amorphous silicon film containing silicon atoms as principal components, or an amorphous deposition film of amorphous silicon supplemented with, for example, hydrogen and/or halogen (for example fluorine and chlorine) has been proposed as a high-performance, highly durable and non-polluting electrophotographic photosensitive member, some of which being practically used. U.S. Pat. No. 4,265,991 also discloses a technology for the electrophotographic photosensitive member whose photoconductive layer is mainly composed of amorphous silicon.
Many methods such as a sputtering method, and methods for decomposing material gases by heat (heat CVD method), light (light CVD method) and plasma (plasma CVD method) have been known in the art for depositing non-crystalline films containing silicon atoms as principal components as described above.
The plasma CVD method, by which the material gas is decomposed by plasma generated by a high-frequency or microwave glow discharge to deposit thin films on the substrate, is most suitable for depositing an amorphous silicon film for the electrophotographic photosensitive member. Practical applications of these methods have been aggressively developed in recent years. Among the CVD methods, the plasma CVD method advantage of decomposition by microwave glow discharge, or the microwave plasma CVD method, has been recently noticed as an industrial method for depositing a film.
The microwave plasma CVD method is advantageous over other methods in its high deposition rate and high conversion efficiency of material gases. One example of this microwave plasma CVD based on the advantages as described above is described in U.S. Pat. No. 4,504,518. The patent described above discloses that a good quality deposition film is obtained with a high deposition rate by the microwave plasma CVD method in a low pressure of 0.1 Torr (13.3 Pa).
A technology for improving the material gas conversion efficiency by the microwave plasma CVD method is disclosed in Japanese Patent Publication Laid-open No. 60-186849. In the technology disclosed in the patent publication described above, an inner chamber (or a discharge space) is formed by disposing the substrate so as to surround an introduction device of microwave energy to obtain a high conversion efficiency of the material gas.
Japanese Patent Publication Laid-open No. 61-283116 discloses an improved microwave technology for producing a semiconductor element. According to the technology disclosed in the patent publication above, an electrode (a bias electrode) for controlling plasma potential is provided in the discharge space. Characteristics of the deposition film are improved by depositing the film while controlling ion impact to the deposition film by applying a desired voltage (a bias voltage) to the bias electrode.
However, there remain some problems to be solved in the electrophotographic photosensitive member formed by the method as described above. One problem is how to prevent abnormal growth in the deposition film.
While abnormal growth portions are sometimes observed in the deposition film grown on the substrate, the portions have a minute area and possess insufficient surface charge. Generation of these abnormal growth portions is especially obvious in the amorphous silicon formed by the plasma CVD method. Generation of such portions possessing insufficient surface charge has been prevented by optimizing surface machining conditions, surface cleaning conditions and deposition conditions.
The following situations have been imposed on the technology:
1) Definition of positive images has been improved in response to the requirements for high image quality of the electrophotographic apparatus; and
2) Electrification conditions have became severe as a result of making copy machines high speed. Consequently, improvement of image quality at the abnormal growth portions has been required since the portions possessing insufficient electric charges substantially have a large influence on the peripheral potential.
The effect of abnormal growth on the image quality has been a small matter since a conventional electrophotographic apparatus is mainly used for copying only printed letters in a typescript (so-called line copy). However, since image qualities of the copy machine have been improved in recent years, copying many original documents containing half-tone images such as photographs is required. Therefore, for complying with these requirements, an electrophotographic photosensitive member containing a small number of abnormal growth portions is currently required. Since the effect of the abnormal growth portions on the image quality is more clearly visualized in the printed images in currently spreading color copy machines, an electrophotographic photosensitive member containing small number of abnormal growth portions is especially required.
The abnormal growth portions are so minute that localization of them is difficult even by a conductivity measurement using an electrode. When the photosensitive member is electrified, exposed and developed by integrating the substrate having the deposition film containing the abnormal growth portions into an electrophotographic process using an electrophotographic photosensitive member, especially when a uniform half-tone image is formed, images of a small potential difference ascribed to the abnormal growth portions on the surface of the electrophotographic photosensitive member may be clearly visualized.
The effect of the abnormal growth portions on the image becomes especially evident in the electrophotographic photosensitive member manufactured by the plasma CVD method, as compared with a Se electrophotographic photosensitive member manufactured by a vacuum deposition method or an OPC electrophotographic photosensitive member manufactured by a blade coating method or dipping method. However, productivity as well as repeatability of the plasma CVD method for manufacturing the electrophotograph are high, besides having wide applicability since the film can be deposited by precisely adjusting its thickness. Accordingly, highly efficient production of high quality substrates is possible when the plasma CVD method is further improved.
Solar cells are another example of the device that can be manufactured by the plasma CVD method other than the electrophotographic photosensitive member. However, overall performance, or the overall photoelectric conversion efficiency, of the solar cell is practically not affected even when the abnormal growth portions are finely distributed at specific locations on the substrate, causing subtle differences of the potential among the abnormal growth portions and other portions. Moreover, such practical problems as the quantity of generated electricity may be solved and desired specification can be attained by post-treatment in the solar cell, even when a small number of abnormal growth portions may exist. In the electrophotographic photosensitive member, on the contrary, the presence of a small number of abnormal growth portions as described above may affect the image quality. Therefore, generation of the abnormal growth portions should be especially prevented in the deposition step.
The second problem is to provide an effective cleaning method using an aqueous solvent. It has been desirable in recent years to avoid use of chlorinated solvents from the view point of preservation of the environment, and the chlorinated solvents have been replaced by aqueous solvents. However, oils and dusts floating on the surface of the cleaning liquid are liable to adhere again and contaminate the cleaning subject after cleaning, when the cleaning subject is pulled up from the cleaning vessel after cleaning with the aqueous cleaning solvent. Accordingly, an effective cleaning method using the aqueous solvent is desired, in order to efficiently wash the cleaning subject by enhancing the ability for cleaning optical parts, electronic parts, mechanical parts and precision parts and preventing the oils and dusts that have been once removed from adhering on the cleaning subject again.
The third problem is to prevent corrosion of the substrates by washing with aqueous solvents. Especially when an aluminum substrate for the electrophotographic photosensitive member as an example of the cleaning subject is washed with water, galvanic batteries are formed among impurities and peripheral aluminum, where no impurities exist, at the portions containing many impurities such as Si partially protruding from the surface of the aluminum, accelerating corrosion of the surface of the substrate. While generation of corrosion has been prevented by using an aqueous carbon dioxide solution as a cleaning solvent, a device for allowing carbon dioxide to dissolve in the cleaning solvent makes the cleaning apparatus to be complicated and therefore cleaning cost is increased. Accordingly, the construction of the apparatus should be more simplified and the cleaning cost should be reduced.
The fourth problem is to suppress irregular cleaning along the longitudinal direction from appearing when a long member along the longitudinal direction such as the substrate of the electrophotographic photosensitive member is pulled up from the cleaning solvent.
Accordingly, the object of the present invention is to provide a method for effectively washing a cleaning subject. In more detail, the object of the present invention is to provide a high performance electrophotographic photosensitive member containing a small number of irregular growth portions and a method for manufacturing the same, wherein irregular cleaning of the substrate is suppressed while preventing corrosion of aluminum.
The foregoing objects can be attained by the following means. The present invention proposes a cleaning method for enhancing cleaning ability by effectively cleaning the cleaning subject, a cleaning apparatus, and an electrophotographic photosensitive member and a method for manufacturing the same.
In a first aspect, the present invention provides a method for cleaning a cleaning subject by allowing a liquid filled in a vessel to overflow, wherein the cleaning subject is cleaned by pulling up the cleaning subject from the liquid filled in the vessel while allowing the liquid to overflow, or wherein the cleaning subject is cleaned by pulling up the cleaning subject from the liquid while increasing the flow rate of the overflowing liquid.
In accordance with another aspect of the present invention, there is provided a cleaning apparatus of a cleaning subject comprising a first vessel for containing a liquid, a flow rate control device for allowing the liquid to overflow from the vessel, a circulation device for feeding the overflow liquid to the vessel again, and a second vessel provided between the first vessel and the liquid circulation device.
In accordance with a further aspect of the present invention, there is provided a method for cleaning the substrate by allowing a liquid filled in a vessel to overflow, wherein the substrate is cleaned by pulling up the substrate from the liquid filled in the vessel while allowing the liquid to overflow from the vessel.